Plot

Investigating strange frequencies from Earth's core, scientists unearth a living rock beneath a volcano. It craves hormones produced by human fear, leading them to abduct girls, sacrificing them to sustain the rock.

A scientist notices strange frequencies coming from within Earth. He and his assistants discover a living rock underneath a volcano. They bring the living rock to their laboratory and discover that in order to survive, it needs the hormones that are produced by humans when they are afraid. They then abduct and sacrifice young girls to the living rock in order to keep it alive.—[email protected]

Prologue: Dr. Carl Mandel [Boris Karloff], an aging scientist, has spent his life looking for answers to the secrets of the universe. When his radio telescopes pick up patterned transmissions coming from underneath a volcano, he sends his assistants - Mark [Carlos East] and his daughter Corinne [Julissa] - to find them while he communicates with them from his laboratory, where his faithful colleague and psychologist companion Helga [Isela Vega] makes sure that he takes his medicine and gets his sleep.

Months later. Mark and Corinne have found the source of the transmissions and brought it back to the laboratory. It is a rock, fashioned from what Mandel thinks might be "primordial plasma," that is able to communicate through an interface with Mandel's computer. It promises great information about the universe, such as the location of diamonds, but first it must be fed. It feeds on hormones that are released into the blood when a human is experiencing great fear, so Mandel and Helga have built a "fear chamber" in order to procure the hormones that are needed by the rock.

Under the guise of being an employment agency where young women are solicited for potential foreign jobs and given lodging during the testing period, Helga chooses suitable donors to be awakened during the night and made to run through the fear chamber (a maze filled with skeletons, spiders, and scenes of torture) until they faint from fear. Then Mandel, aided by Helga, Corinne, Mark, and three other assistants - a dwarf [Santanón], a bearded man wearing a turban, and a retarded strongman named Roland [Yerye Beirute] - extract just enough blood to feed the rock, but not harm the donor. In fact, most of the donors awake the next morning thinking that they have merely had a bad dream. None of the donors are ever harmed...well, except for one girl which Helga has kept herself from telling about to Mandel, who is extremely adamant about not taking any human lives.

As the experiments continue, however, the rock seems to be becoming more and more hungry. It has also evolved a tentacle which allows it to reach out and grab things. When it uses that tentacle to grab a victim, draw her in, and feed on her blood, Mandel realizes the potential of the rock to become murderous and cuts off the heat source that it needs to survive. The rock responds by interfacing with the computer as though it is finally willing to tell its secrets, but Mandel begins to pull out the power cords anyway. The strain of pulling out all of the cords causes Mandel to collapse.

With Mandel confined to his bed, Helga refuses to let the rock die. She arranges some time away for Corinne and Mark and enlists Roland's help in killing the dwarf and the turbaned man. Between just the two of them, Helga and Roland revive the rock and provide it with all the blood that it wants. It thanks them for their help by spitting out some garbled data about diamonds.

[Roland likes diamonds. Roland wants diamonds. Lots of diamonds. Roland is friends with the rock. The rock talks to Roland, and Roland talks to the rock. The rock tells Roland that he will be king of the world. Roland wants to be king of world and have all the diamonds!]

After reanalyzing the data, Helga has come to a chilling conclusion. The rock's purpose has been not to educate scientists about the secrets of the universe, but to learn how to live on the surface of Earth. It is now ready to relay its findings to others like itself who live near the Earth's core. Their plan is to take over Earth and feed on both the blood and the fear of humans.

Helga wants to kill the rock, but Roland will not let this happen to his friend, so he chases Helga through the fear chamber and allows the rock to feed on her. Roland then drives off in his car yelling, "I'm going to be king of the world!" just as Corinne and Mark return home. Corinne runs straight down to the laboratory, where she finds Helga with the life sucked out of her and her father feverishly typing a new program into the computer. The rock grabs Corinne with its tentacle. Mandel reminds her that the rock feeds on fear and tells her not to be afraid. As Corinne repeats over and over again to herself "I am not afraid," Mark takes over for Mandel on the computer, fighting to run the program before the rock can develop its own internal circuits, which will render it capable of living. Mark is successful. As the computer wiring around them goes up in flames, Mandel explains that the program required accessing every step of the rock's growth process and then reversing it. The now-dead rock begins to crumble into pieces as Mandel expresses the hope that they were able to stop it before it relayed its information to others like itself. Meanwhile, Roland can be seen running around under the volcano, shouting "Diamonds! King of the world! Diamonds!" The volcano then erupts. [original synopsis by bj_kuehl]